Hi, sorry, nobody replied sooner. It is what commonly known as nose rub. It happens for multiple reasons, stress is most common cause, so the question. Can you please describe the husbandry, size of the tank, decor, picture would be great to see too. unless the cause of the problem is removed it will keep reappearing and possibly getting worse and worse.

Treatment - best is to get flamazine, it's silver sulfadiazine cream, should be available at vet clinics, human pharmacies too. It is used in human medicine for burns, etc. If you can't find it then any antibiotic cream without pain killers should work. If not you need systemic antibiotics.